While Firefox, Safari and Opera also support the Do Not Track header, which tells websites and their advertising partners not to track your movements around the web, IE 10 will be the first to enable it by default.

Brendon Lynch, Microsoft’s Chief Privacy Officer, says that “DNT will be enabled in the ‘Express Settings’ portion of the Windows 8 set-up experience…. There, customers will also be given a ‘Customize’ option, allowing them to easily switch DNT off if they’d like.”

Turning DNT on by default in Internet Explorer 10 means that for the first time a significant number of users will be opting out of ad tracking.

Behavioral tracking, as such practices are often called, is common on the web. Advertisers use cookies to track your clicks, watching which sites you visit, what you buy and even, in the case of mobile browsers, where you go. Often the sites tracking you are not just the sites you’ve actually visited, but third-party sites running ads on those pages.

Privacy advocates at Mozilla created DNT as a way for users to tell advertisers to stop the tracking. The W3C is in the process of turning DNT into a web standard.

Of course for DNT to work it requires advertisers to respect it. Despite the fact that DNT is counter to their interests, several of the major ad groups on the web have pledged to respect it. But thus far, because DNT is off by default in all the web browsers that support it, use is not widespread. Advertisers know that very few users change the default settings, so most people are unlikely to ever enable DNT, making support a less threatening proposition for advertisers.

IE 10 will be the first real test of whether or not ad groups will continue to support DNT. Microsoft took quite a bit of heat from ad groups back when it first announced that DNT would be on by default. Microsoft has defended its choice, arguing that DNT is good for users. As Lynch writes, “our approach to DNT in IE10 is part of our commitment to privacy by design and putting people first. We believe consumers should have more control over how data about their online behavior is tracked, shared, and used.”